The invention relates generally to a method for making a catalyst composition. In particular, the invention relates to a method for making a catalyst composition useful for reactions that result in reduced emissions of nitrogen oxides.
Regulations continue to evolve regarding the reduction of the oxide gases of nitrogen (NOx) for diesel engines in trucks and locomotives, since NOx gases may be undesirable. A NOx reduction solution may include treating diesel engine exhaust with a catalyst that can reduce NOx to N2 and O2, using a reductant. This process may be referred to as selective catalytic reduction or SCR.
In selective catalytic reduction (SCR), a reductant, such as ammonia, is injected into the exhaust gas stream to react with NOx in contact with a catalyst. Selective catalytic reduction catalysts may include catalytic metals disposed upon a porous, high-surface area carrier support such as gamma alumina. Three general types of catalysts have been used in these systems. They include base metal systems, noble metal systems, and zeolite systems, and selection of a specific system often depends on temperatures for the underlying reactions. For example, silver-containing alumina is known for being useful for the selective catalytic reduction (SCR) of NOx, using hydrocarbon reductants.
Catalytic activity in alumina-supported catalysts usually depends on surface area, as well as on the pore size and pore volume of the alumina carrier. The effective temperature of catalytic performance favorably decreases with an increase in the surface area of the alumina carrier. However, these catalysts may not function effectively if the structure and/or efficacy of the carrier support are compromised during manufacture.
It would be desirable to develop new methods for processing high performance catalyst compositions that address some of these issues.